The role of latent Sphaeropsis sapinea infections in post-hail associated die-back of Pinus patula

Sphaeropsis sapinea is an economically important pathogen of pines in South Africa. The most serious disease caused by this fungus is die-back of Pinus patula and Pinus radiata after hail. In this study, we investigate the role of latent S. sapinea infections in seed cones of P patula in post-hail associated die-back. R patula seed cones were found to be infected during the second year of development. Extensive colonization of all cone tissues occurred in the third year when cones mature. prior to seed discharge. Vegetative compatibility tests showed that S. sapinea is present as a single vegetatively compatible group in the third year seed cones. The presence of S. sapinea in colonized third year seed cones apparently result from a single successful infection in each cone. The probable role of latent infections by S. sapinea was considered in a case study of hail-damaged P. patula trees of three age classes. Mortality was most severe in a stand of 25-year-old trees (92%) followed by a stand of 14-year-old trees (32%) and a 5-year-old stand (9%). Isolations from diseased trees showed that S. sapinea could be recovered from darkly stained branch pith, which was continuous with infected pith in third year seed cones. In contrast, the fungus was absent in the non-discolored pith of branches on healthy trees of the same age. Our results indicate that S. sapinea infects branch pith tissue directly from previously infected, attached seed cones to cause rapid die-back and mortality of hail-damaged trees. (C) 2002 Elsevier Science B.V. All rights reserved.